旋轉效應對垂直電場作用下具導電梯度之水平流體層穩定特性分析

Abstract

具有導電梯度之溶液受電力作用的穩定現象之研究，源於所謂的等電位聚焦電泳(Isoelectric focusing)分離技術。此技術常被應用於蛋白質等複雜混合物之分離，亦即透過外加電場的作用，不同組成的化合物會聚集在溶液中不同pH值處，進而達成分離目的。原則上，施加電場越大，則分離效果越佳。但當電場超過某一臨界值時，電力將有足夠的動能克服黏滯力而引起不穩定流動，最終導致流體的混合與分離的失效，這是該技術應用上要極力避免的。近來，許多學者致力於利用流場穩定性分析方法，探求不穩定機制的來源，或描繪各物理參數圖以輔助設計，或加入額外機制來進一步改善裝置性能。在這方面已有許多可行的構想與顯著的進展被提出。本研究乃著重於理論分析探討外加旋轉效應的影響，希望藉由旋轉能使流場更加穩定。分析結果顯示，適當的旋轉效應的確可以有效增加流場的穩定性，進而提高等電位聚焦電泳分離效率。

Interest in electrohydrodynamic instability of a solution with an electric conductivity stems from the so-called isoelectric focusing (IEF) technique, which is a separation process used to isolate and purify biological materials such as protein. Under imposing an appropriate electric field, materials of different composition will gather at places of different pH values and eventually the materials can be separated successfully. In general, a higher electric field makes a more efficient separation. However, once the applied electric field exceeds a critical value, the fluid will acquire sufficient energy to overcome the viscous force and becomes unstable, that is the most undesired situation. Recently, many researchers are devoted to explore the destabilizing mechanism by the hydrodynamic instability analysis. They either depicted parametric maps for optimizing design or imposed additional mechanisms on the system for the improvement of performance. Many good ideas have been proposed and a number of related achievements have also been reported. This study aims to investigate the dependence of the rotational effect on the stability of conducting fluids. The result shows that an imposition of a constant angular velocity can suppress the growth of disturbances and stabilize the flow. This concludes that the rotation effect can indeed improve the efficiency of IEF process.